Final answer:
The frequency of light remains unchanged as it passes through a boundary, which is a characteristic shared with mechanical waves.
Step-by-step explanation:
The property of light that stays the same as it passes through a boundary is its frequency. This is also true for mechanical waves; frequency does not change upon crossing the boundary between two media. When light crosses a boundary at a non-normal angle, its speed changes due to the different optical densities of the new medium. The result is a change in the wavelength and the direction of the wave, a phenomenon known as refraction. However, its frequency remains constant, just as mechanical waves reflect off a rigid surface or interfere with each other, retaining their frequency.
Essential Knowledge 6.E.3 indicates that when light travels across a boundary from one transparent material to another, its speed of propagation changes, leading to refraction. Nevertheless, the frequency of the light wave does not alter. This concept is fundamental to understanding wave behavior across different mediums and is instrumental in many applications, including optics and telecommunications.